1. Field of the Invention
This invention is concerned with improvements in or relating to internal mixing machines and more particularly to rotors for use therein.
2. Prior Art
One type of mixer which is commonly used for compounding rubber or plastic materials is known as an internal mixer. U.S. Pat. Nos. 3,704,866 to Mosher et al, and 3,154,808 to Ahlefeld, Jr. et al, both assigned to the assignee of the present invention, and herein incorporated by reference, show internal mixing apparatus of the type discussed for use with the present invention. This type of internal mixer is manufactured by the present assignee under the trademark "BANBURY". The internal mixers comprise a composite mixing chamber formed by two parallel transversely interconnected cylindrically shaped chamber portions each of circular cross section arranged so that, in cross section, the mixing chamber has approximately the shape of a FIG. 8. A mixing rotor is mounted for rotation, one in each chamber portion of circular cross section. A centrally disposed inlet opening for internal mixers is generally provided through an upper wall of the mixing chamber between the two rotors. A centrally disposed outlet opening from the mixing chamber is disposed below the rotors through the wall of the mixing chamber. When the outlet opening is closed by a suitable closure member, material to be mixed is introduced to the mixing chamber through the inlet opening and forced into the mixing chamber and into engagement with the rotating rotors under pressure applied through a ram. When all the material introduced into the mixing chamber has been adequately mixed, the closure member closing the outlet opening is removed to allow the mixed material to discharge through the outlet opening. Such internal mixers perform satisfactorily on a wide range of materials; however, it has been found that when the material to be mixed includes large chunks of stiff and rigid material, the chunks have sometimes become lodged in a position in the mixing chamber in which the rotors are jammed and are prevented from rotating. This jamming in the prior art internal mixers will usually cause considerable damage to the mixer. For example when using internal mixers to plasticize and recompound scrap polyvinyl chloride, chunks causing jamming of the rotors has occured to the detriment of the mixer.
It is an object of the present invention to eliminate jamming of the rotor blades by chunks of material lodged therebetween.